Method of atomic layer etching using functional group-containing fluorocarbon

ABSTRACT

A method of atomic layer etching (ALE) uses a cycle including: continuously providing a noble gas; providing a pulse of an etchant gas to the reaction space to chemisorb the etchant gas in an unexcited state in a self-limiting manner on a surface of a substrate in the reaction space; and providing a pulse of a reactive species of a noble gas in the reaction space to contact the etchant gas-chemisorbed surface of the substrate with the reactive species so that the layer on the substrate is etched. The etchant gas is a fluorocarbon gas containing a functional group with a polarity.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention generally relates to a method of atomic layeretching (ALE), particularly to a method of ALE using a functionalgroup-containing fluorocarbon etchant.

Description of the Related Art

Atomic layer etching (ALE) is cyclic, atomic layer-level etching usingan etchant gas adsorbed on a target film and reacted with excitedreaction species, as disclosed in Japanese Patent Laid-open PublicationNo. 2013-235912 and No. 2014-522104. As compared with conventionaletching technology, ALE can perform precise, atomic layer-levelcontinuous etching on a sub-nanometer order to form fine, narrowconvex-concave patterns and may be suitable for e.g., double-patterningprocesses. As an etchant gas, Cl₂, HCl, CHF₃, CH₂F₂, CH₃F, H₂, BCL₃,SiCl₄, Br₂, HBr, NF₃, CF₄, C₂F₆, C₄F₈, SF₆, O₂, SO₂, COS, etc. areknown. However, it is revealed that in-plane uniformity of etching of afilm on a substrate by ALE is not satisfactory when etching an oxide ornitride mineral film such as silicon oxide or nitride film.

Any discussion of problems and solutions in relation to the related arthas been included in this disclosure solely for the purposes ofproviding a context for the present invention, and should not be takenas an admission that any or all of the discussion was known at the timethe invention was made.

SUMMARY OF THE INVENTION

When etching Si or GaAs by ALE using Cl₂ as an etchant gas, relativelygood in-plane uniformity of etching can be obtained. However, whenetching a silicon oxide or silicon nitride film by ALE using afluorocarbon such as C₄F₈ as an etchant gas, good in-plane uniformity ofetching is not obtained. This is because the etchant gas is adsorbed ona surface of a substrate through physical adsorption, not chemicaladsorption, despite the fact that conventionally, the adsorption of anetchant gas is sometimes called “chemisorption.” That is, conventionalALE etches a metal or silicon oxide or nitride film by etchant gasphysically adsorbed on its surface, wherein the adsorbed etchant gasreacts with excited species, and also by etchant gas which remains inthe reaction space after being purged, causing gas-phase etching. As aresult, in-plane uniformity of etching suffers. If an etchant gas ischemisorbed on a surface of a substrate, the adsorption is“chemisorption” which is chemical saturation adsorption which is aself-limiting adsorption reaction process, wherein the amount ofdeposited etchant gas molecules is determined by the number of reactivesurface sites and is independent of the precursor exposure aftersaturation, and a supply of the etchant gas is such that the reactivesurface sites are saturated thereby per cycle (i.e., the etchant gasadsorbed on a surface per cycle has a one-molecule thickness onprinciple). When chemisorption of an etchant gas on a substrate surfaceoccurs, high in-plane uniformity of etching can be achieved.Conventional ALE, even though it calls adsorption “chemisorption,” infact adsorbs an etchant gas on a substrate surface (e.g., SiO₂ and SiN)by physical adsorption. If adsorption of an etchant gas ischemisorption, in-plane uniformity of etching should logically be highand also the etch rate per cycle should not be affected by the flow rateof the etchant gas or the duration of a pulse of etchant gas flow afterthe surface is saturated by etchant gas molecules. However, none ofconventional etchant gases satisfies the above.

In some embodiments, a fluorocarbon which contains a functional groupwith a polarity is used as an etchant gas. The functionalgroup-containing fluorocarbon has a structure where a fluorocarbonconstitutes a basic skeleton, and at least one reactive functional groupis attached thereto as a terminal group. The functional group includes ahydroxyl group (—OH) and an amino group (—NH₂), for example, and theetchant gas is chemically adsorbed on a surface of a substrate based onthe principle of substitution reaction or hydrogen bonding, etc. Theadsorption of the etchant gas takes place by the terminal group on thesubstrate surface, and since the fluorocarbon basic skeleton itself isnon-reactive to adsorption reaction, only one layer of the etchant gasmolecules can be formed on the substrate surface. In this disclosure,chemical adsorption is referred to as chemisorption or self-limitingadsorption.

In some embodiments, by adsorbing an etchant gas on a surface of a metalor silicon oxide or nitride substrate (e.g., SiO₂ substrate) in aself-limiting manner, ALE cycles (e.g., plasma-enhanced ALE or PEALE,thermal ALE, radical ALE) are performed to etch the surface, therebyimproving in-plane uniformity of etching. In some embodiments, such anetchant is typically liquid at room temperature, the etchant isintroduced into a reaction chamber using a flow-path switching (FPS)method wherein a carrier gas can continuously flow into the reactionchamber and can carry etchant gas in pulses by switching a main line anda detour line provided with a reservoir storing a liquid etchantprecursor.

Additionally, since the functional group-containing fluorocarbon caneffectively be chemisorbed on a metal or silicon oxide or nitrate film,deposition of a film containing fluorocarbon can be conducted by ALD, inplace of etching, by using a proper reactant gas such as hydrogen in anexcited state (e.g., Ar/H₂ plasma).

For purposes of summarizing aspects of the invention and the advantagesachieved over the related art, certain objects and advantages of theinvention are described in this disclosure. Of course, it is to beunderstood that not necessarily all such objects or advantages may beachieved in accordance with any particular embodiment of the invention.Thus, for example, those skilled in the art will recognize that theinvention may be embodied or carried out in a manner that achieves oroptimizes one advantage or group of advantages as taught herein withoutnecessarily achieving other objects or advantages as may be taught orsuggested herein.

Further aspects, features and advantages of this invention will becomeapparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof necessary fee.

These and other features of this invention will now be described withreference to the drawings of preferred embodiments which are intended toillustrate and not to limit the invention. The drawings are greatlysimplified for illustrative purposes and are not necessarily to scale.

FIG. 1A is a schematic representation of a PEALD (plasma-enhanced atomiclayer deposition) apparatus for depositing a protective film usable inan embodiment of the present invention.

FIG. 1B illustrates a schematic representation of a precursor supplysystem using a flow-pass switching (FPS) system usable in an embodimentof the present invention.

FIG. 2 shows a schematic process sequence of PEALE in one cycleaccording to an embodiment of the present invention wherein a stepillustrated in a cell represents an ON state whereas no step illustratedin a cell represents an OFF state, and the width of each cell does notrepresent duration of each process.

FIG. 3 shows a schematic process sequence of PEALD in one cycle incombination with a schematic process sequence of PEALE in one cycleaccording to an embodiment of the present invention wherein a cell ingray represents an ON state whereas a cell in white represents an OFFstate, and the width of each column does not represent duration of eachprocess.

FIG. 4A is a graph showing the relationship between etching rate percycle (EPC) (nm/cycle) and etchant gas feed time per cycle (seconds)according to an embodiment of the present invention (“Ex. 1 (F=3)” and“Ex. 2 (F=6)”) and a comparative example (“Comp. Ex.”).

FIG. 4B is a graph showing the relationship between etching rate percycle (EPC) (nm/cycle) and etchant gas feed time per cycle (seconds)when changing the flow rate of etchant gas (C₂F₆) according tocomparative examples.

FIGS. 5A, 5B, and 5C are Scanning Electron Microscope (SEM) photographsof cross-sectional views of conformal silicon oxide films wherein FIG.5A shows a silicon oxide film prior to PEALE cycles, FIG. 5B shows asilicon oxide film after the PEALE cycles using C2F6, and FIG. 5C showsa silicon oxide film after the PEALE cycles using 2,2,2-Trifluoroethanolaccording to an embodiment of the present invention.

FIG. 6A shows color images of thin-film etched thickness profilemeasurement by 2D color map analysis of a film according to acomparative example.

FIG. 6B shows color images of thin-film etched thickness profilemeasurement by 2D color map analysis of a film according to anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

In this disclosure, “gas” may include vaporized solid and/or liquid andmay be constituted by a single gas or a mixture of gases. In thisdisclosure, a process gas introduced to a reaction chamber through ashowerhead may be comprised of, consist essentially of, or consist of anetchant gas and an additive gas. The additive gas typically includes adilution gas for diluting the etchant gas and reacting with the etchantgas when in an excited state. The etchant gas can be introduced with acarrier gas such as a noble gas. Also, a gas other than the process gas,i.e., a gas introduced without passing through the showerhead, may beused for, e.g., sealing the reaction space, which includes a seal gassuch as a noble gas. In some embodiments, the term “etchant gas” refersgenerally to at least one gaseous or vaporized compound thatparticipates in etching reaction that etches a layer on a substrate, andparticularly to at least one compound that chemisorbs onto the layer ina non-excited state and etches the layer when being activated, whereasthe term “reactant gas” refers to at least one gaseous or vaporizedcompound that contributes to activation of the etchant gas or catalyzesan etching reaction by the etchant gas. The term “etchant gas” refers toan active gas without a carrier gas, or a mixture of an active gas and acarrier gas, depending on the context. The dilution gas and/or carriergas can serve as “reactant gas”. The term “carrier gas” refers to aninert or inactive gas in a non-excited state which carries an etchantgas to the reaction space in a mixed state and enters the reaction spaceas a mixed gas including the etchant gas. The inert gas and the etchantgas can converge as a mixed gas anywhere upstream of the reaction space,e.g., (a) in an etchant gas line upstream of a mass flow controllerprovided in the etchant gas line, wherein the inert gas is provided as acarrier gas or purge gas flowing through the etchant gas line, (b) in anetchant gas line downstream of a mass flow controller provided in theetchant gas line but upstream of a gas manifold where all or mainprocess gases converge, wherein the inert gas is provided as a part ofthe etchant gas (as a carrier gas or purge gas), and/or (c) in a gasmanifold where all or main process gases converge, wherein the inert gasflows in a reactant gas line as a reactant gas or purge gas upstream ofthe gas manifold. In the above, typically, (a) is rare. Thus, the inertgas can serve as a carrier gas (as a part of etchant gas) and/or atleast a part of a reactant gas, wherein the above gases can serve alsoas purge gases.

In some embodiments, “film” refers to a layer continuously extending ina direction perpendicular to a thickness direction substantially withoutpinholes to cover an entire target or concerned surface, or simply alayer covering a target or concerned surface. In some embodiments,“layer” refers to a structure having a certain thickness formed on asurface or a synonym of film or a non-film structure. A film or layermay be constituted by a discrete single film or layer having certaincharacteristics or multiple films or layers, and a boundary betweenadjacent films or layers may or may not be clear and may be establishedbased on physical, chemical, and/or any other characteristics, formationprocesses or sequence, and/or functions or purposes of the adjacentfilms or layers.

Further, in this disclosure, any two numbers of a variable canconstitute a workable range of the variable as the workable range can bedetermined based on routine work, and any ranges indicated may includeor exclude the endpoints. Additionally, any values of variablesindicated (regardless of whether they are indicated with “about” or not)may refer to precise values or approximate values and includeequivalents, and may refer to average, median, representative, majority,etc. in some embodiments. Additionally, the terms “constituted by” and“having” refer independently to “typically or broadly comprising”,“comprising”, “consisting essentially of”, or “consisting of” in someembodiments. Further, an article “a” or “an” refers to a species or agenus including multiple species. In this disclosure, any definedmeanings do not necessarily exclude ordinary and customary meanings insome embodiments.

In the present disclosure where conditions and/or structures are notspecified, the skilled artisan in the art can readily provide suchconditions and/or structures, in view of the present disclosure, as amatter of routine experimentation. In all of the disclosed embodiments,any element used in an embodiment can be replaced with any elementsequivalent thereto, including those explicitly, necessarily, orinherently disclosed herein, for the intended purposes. Further, thepresent invention can equally be applied to apparatuses and methods.

The embodiments will be explained with respect to preferred embodiments.However, the present invention is not limited to the preferredembodiments.

Some embodiments provide a method for etching a layer on a substrateplaced in a reaction space by an atomic layer etching (ALE) processwhich comprises at least one etching cycle, wherein an etching cyclecomprises: (i) continuously providing a noble gas (e.g., flowing atleast as a carrier gas for an etchant gas) into the reaction space; (ii)providing a pulse of an etchant gas (e.g., into the continuous noble gasflow upstream of the reaction space) to chemisorb the etchant gas in anunexcited state in a self-limiting manner on a surface of the substratein the reaction space, said etchant gas being a fluorocarbon gascontaining a functional group with a polarity, said surface of thesubstrate being constituted by an oxide or nitride mineral (referred toalso as “an oxide or nitride ceramic”); and (iii) providing a pulse of areactive species of a noble gas in the reaction space to contact theetchant gas-chemisorbed surface of the substrate with the reactivespecies so that the surface of the layer on the substrate is etched. Inthe above, the term “continuously” refers to without interruption inspace (e.g., uninterrupted supply over the substrate), withoutinterruption in flow (e.g., uninterrupted inflow), and/or at a constantrate (the term need not satisfy all of the foregoing simultaneously),depending on the embodiment. In some embodiments, “continuous” flow hasa constant flow rate (alternatively, even though the flow is“continuous”, its flow rate may be changed with time). The term“chemisorption” refers to adsorption of gas molecules chemically on asurface of a film by force stronger than Van der Waals force, i.e.,physical adsorption. In some embodiments, chemisorption includes notonly adsorption as a result of chemical reaction between terminal groupsof gas molecules and the film surface, but also adsorption via hydrogenbonding or bonding equivalent thereto including electrostatic adsorptionusing the polarity of the terminal groups of the gas molecules. In someembodiments, chemisorption means adsorption which is stronger thanphysical adsorption. The term “self-limiting manner” refers to a mannerwherein the amount of deposited gas molecules is determined by thenumber of reactive surface sites and is independent of the gas exposureafter saturation, and a supply of the gas is such that the reactivesurface sites are saturated thereby per cycle (i.e., the gas adsorbed ona surface per cycle has a one-molecule thickness on principle).

In some embodiments, the functional group contained in the etchant gasis selected from the group consisting of a hydroxyl group, amino group,ether group, ketone group, and carboxyl group. For example, when theetchant gas is CF₃CH₂OH and the substrate surface is constituted bysilicon oxide, chemisorption of the etchant gas on a substrate surfacemay take place through the following chemical reaction:CF₃CH₂—OH+Si—OH→CF₃CH₂—O—Si+H₂O

Since the functional group has a polarity, it can be adsorbed on asubstrate surface using the polarity. Preferably, the functional groupcontains oxygen or nitrogen. In some embodiments, the etchant gas is aperfluorocarbon gas. In some embodiments, the etchant gas is CF₃ROH,C₃F₇ROH, C₃F₇RNH₂, and/or (CF₃R)₂O wherein R represents an alkylenegroup having 1, 2, 3, or 4 carbon atoms. For example, the etchant gas isselected from the group consisting of CF₃CH₂OH, C₃F₇CH₂OH, C₃F₇CH₂NH₂,and/or (CF₃CH₂)₂O. Preferably, the etchant gas contains more than threefluorine atoms in its molecule. In some embodiments, no gas other thanthe etchant gas flows as an etchant gas throughout the ALE process.Alternatively, in some embodiments, any of known etchant gases such asCl₂, HCl, CHF₃, CH₂F₂, CH₃F, H₂, BCL₃, SiCl₄, Br₂, HBr, NF₃, CF₄, C₂F₆,C₄F₈, SF₆, O₂, SO₂, and COS can be used as a secondary etchant gas incombination with the functional group-containing fluorocarbon.

In some embodiments, while providing the reactive species of the noblegas, no reactive species of O₂, H₂, or N₂ are present in the reactionspace. When the adsorbed etchant gas reacts with excited species of thenoble gas, fluorine radicals (F*) are generated, which are the mainetching component. However, when reactive species of O₂, H₂, or N₂ arepresent in the reaction space, the reactive species react with fluorineradicals, interfering with or inhibiting the etching reaction. Forexample, an Ar/O₂ plasma or Ar/H₂ plasma does not cause etchingreaction, and a N₂ plasma can cause etching reaction but only at anextremely low etching rate. In some embodiments, the above reactivespecies may be added to the reaction space when the etchant gas containsmore fluorine atoms, or after the cycle of providing the reactivespecies of the noble gas.

In some embodiments, the pulse of the reactive species of the noble gasis provided by applying a pulse of RF power discharge between electrodesdisposed in the reaction space, between which the substrate is placed.The noble gas can be excited by applying a pulse of RF power in-situ orcan be provided to the reaction space as noble gas radicals by a remoteplasma unit. Alternatively, the noble gas can be excited thermally inthe reaction space. In some embodiments, the noble gas is He, Ne, Ar,Kr, and/or Xe, preferably Ar and/or He.

In some embodiments, the oxide or nitride mineral constituting thesurface of the substrate is a metal or silicon oxide or nitride,typically those selected from the group consisting of SiO₂, SiON, SiN,TiO, TiON, TiN, Al₂O₃, and AlN. Any suitable substrate which can beetched by radical fluorine (such as those containing —OH groups on itssurface) can be a target. In some embodiments, SiC may be a target.

In some embodiments, prior to the ALE process, a film is deposited on asubstrate in the reaction space by atomic layer deposition (ALD),wherein the film on the substrate constitutes the surface of thesubstrate subjected to the ALE process, wherein the ALD process and theALE process are conducted continuously in the reaction space. In someembodiments, the reaction space is controlled at a constant pressurethroughout the ALD process and the ALE process.

In some embodiments, a purging period is taken between the pulse of theetchant gas and the pulse of the reactive species of the noble gas toremove excess etchant gas from the reaction space, and a purging periodis taken after the pulse of the reactive species of the noble gas toremove by-products from the reaction space.

In some embodiments, the layer of the substrate has a recess pattern. Insome embodiments, the surface of the substrate is etched isotropically.The etching is “isotropic” when conformality of etched surfaces, whichis a percentage calculated by dividing the etched thickness at asidewall by the etched thickness at a top surface, is 100%±10%.

Additionally, since the functional group-containing fluorocarbon caneffectively be chemisorbed on a metal/silicon oxide or nitrate film,deposition of a film containing fluorocarbon (e.g., CxFy film) can beconducted by ALD, in place of etching, by using a proper reactant gassuch as hydrogen in an excited state (e.g., Ar/H₂ plasma).

Some embodiments will be explained with respect to the drawings.However, the present invention is not limited to the embodiments.

In some embodiments, the process sequence may be set as illustrated inFIG. 2. FIG. 2 shows a schematic process sequence of PEALE in one cycleaccording to an embodiment of the present invention wherein a stepillustrated in a cell represents an ON state whereas no step illustratedin a cell represents an OFF state, and the width of each cell does notrepresent duration of each process. In this embodiment, one cycle ofPEALE comprises “Feed” where an etchant gas is fed to a reaction spacevia a carrier gas which carries the etchant gas without applying RFpower to the reaction space, and also, a dilution gas is fed to thereaction space, thereby chemisorbing the etchant gas onto a surface of asubstrate via self-limiting adsorption; “Purge 1” where no etchant gasis fed to the reaction space, while the carrier gas and dilution gas arecontinuously fed to the reaction space, without applying RF power,thereby removing non-chemisorbed etchant gas and excess gas from thesurface of the substrate; “RF” where RF power is applied to the reactionspace while the carrier gas and dilution gas are continuously fed to thereaction space, without feeding the etchant gas, thereby etching a layeron which the etchant gas is chemisorbed through plasma reaction with thereactant gas; and “Purge 2” where the carrier gas and dilution gas arecontinuously fed to the reaction space, without feeding the etchant gasand without applying RF power to the reaction space, thereby removingby-products and excess gas from the surface of the substrate. Due to thecontinuous flow of the dilution gas and the continuous flow of thecarrier gas entering into the reaction space as a constant stream intowhich the etchant gas is injected intermittently or in pulses, purgingcan be conducted efficiently to remove excess gas and by-productsquickly from the surface of the layer, thereby efficiently continuingmultiple ALE cycles. In some embodiments, the ALE cycles may beconducted under the conditions shown in Table 1 below.

TABLE 1 (the numbers are approximate) Conditions for PEALE Substratetemperature 0 to 400° C. (preferably 20 to 200° C.) Pressure 1 to 1000Pa (preferably 1 to 500 Pa) Noble gas (as a carrier gas Ar and/ordilution gas) Flow rate of carrier gas 100 to 2000 sccm (preferably 1000to (continuous) 2000 sccm) Flow rate of dilution gas 100 to 5000 sccm(preferably 500 to (continuous) 2000 sccm) Etchant gas CF₃CH₂OH,C₃F₇CH₂OH, C₃F₇CH₂NH₂, and/or (CF₃CH₂)₂O Flow rate of etchant gasCorresponding to the flow rate of carrier gas RF power (13.56 MHz) for a50 to 1000 W (preferably 100 to 400 W) 300-mm wafer Duration of “Feed”0.1 to 5 sec. (preferably 0.1 to 0.5 sec.) Duration of “Purge 1” 0.2 to60 sec. (preferably 0.2 to 10 sec.) Duration of “RF” 0.5 to 10 sec.(preferably 1 to 5 sec.) Duration of “Purge 2” 0.05 to 1 sec.(preferably 0.05 to 0.1 sec.) Duration of one cycle 0.85 to 76 sec.(preferably 1.35 to 16.6 sec.) Etching rate per cycle 0.03 to 0.15(preferably 0.05 to 0.10) on (nm/min) top surface

In some embodiments, the process sequence may be set as illustrated inFIG. 3. FIG. 3 shows a schematic process sequence of PEALD in one cyclein combination with a schematic process sequence of PEALE in one cycleaccording to an embodiment of the present invention wherein a cell ingray represents an ON state whereas a cell in white represents an OFFstate, and the width of each column does not represent duration of eachprocess. In this embodiment, one cycle of PEALD comprises “Si-Feed”where a Si-containing precursor gas (Si-precursor) is fed to a reactionspace via a carrier gas which carries the Si-precursor without applyingRF power to the reaction space, and also, a dilution gas and a reactantgas are fed to the reaction space, thereby chemisorbing the etchant gasonto a surface of a substrate via self-limiting adsorption; “Purge”where no Si-precursor is fed to the reaction space, while the carriergas, the dilution gas, and reactant gas are continuously fed to thereaction space, without applying RF power, thereby removingnon-chemisorbed etchant gas and excess gas from the surface of thesubstrate; “RF” where RF power is applied to the reaction space whilethe carrier gas, the dilution gas, and reactant gas are continuously fedto the reaction space, without feeding the Si-precursor, therebydepositing a dielectric layer through plasma surface reaction with thereactant gas in an excited state; and “Purge” where the carrier gas, thedilution gas, and reactant gas are continuously fed to the reactionspace, without feeding the Si-precursor and without applying RF power tothe reaction space, thereby removing by-products and excess gas from thesurface of the substrate. The carrier gas can be constituted by thereactant gas. Due to the continuous flow of the carrier gas enteringinto the reaction space as a constant stream into which the Si-precursoris injected intermittently or in pulses, purging can be conductedefficiently to remove excess gas and by-products quickly from thesurface of the layer, thereby efficiently continuing multiple ALDcycles.

When the reactive species of noble gas are produced using a remoteplasma unit, “RF” in the sequence illustrated in FIG. 2 is replaced byintroduction of noble gas radicals from a remote plasma unit.

In the sequence illustrated in FIG. 3, after the PEALD cycles, the PEALEcycle starts in the same reaction chamber. In this sequence, one cycleof PEALE comprises: “Etchant-Feed” where an etchant precursor is fed tothe reaction space without applying RF power to the reaction space, andalso, the carrier gas and the dilution gas used in the PEALD cycle arecontinuously fed to the reaction space at the constant flow rateswhereas no reactant gas used in the PEALD cycle is fed to the reactionspace, thereby chemisorbing the etchant precursor onto the surface ofthe substrate via self-limiting adsorption; “Purge” where no etchantprecursor is fed to the reaction space, while the carrier gas and thedilution gas are continuously fed to the reaction space, withoutapplying RF power, thereby removing non-chemisorbed etchant precursorand excess gas from the surface of the substrate; “RF” where RF power isapplied to the reaction space while the carrier gas and the dilution gasare continuously fed to the reaction space, without feeding the etchantprecursor, thereby etching a layer on which the etchant precursor ischemisorbed through plasma reaction; and “Purge” where the carrier gasand the dilution gas are continuously fed to the reaction space, withoutfeeding the etchant precursor and without applying RF power to thereaction space, thereby removing by-products and excess gas from thesurface of the substrate. The carrier gas and/or the dilution gas areused as a reactant gas for PEALE. Due to the continuous flow of thecarrier gas and the dilution gas entering into the reaction space as aconstant stream into which the etchant precursor is injectedintermittently or in pulses, purging can be conducted efficiently toremove excess gas and by-products quickly from the surface of the layer,thereby efficiently continuing multiple ALE cycles.

In some embodiments, the carrier gas for the Si-precursor is fed to thereaction chamber through the same gas inlet port, wherein the carriergas, which flows from a gas source through a line fluidically connectedto a reservoir of the Si-precursor in the PEALD cycle, bypasses thereservoir and enters into the reaction chamber through the gas inletport in the PEALE cycle at a constant flow rate. The dilution gas canalso be fed at a constant flow rate throughout the continuousfabrication process constituted by the PEALD cycles and the PEALEcycles. Accordingly, the fluctuation of pressure in the reaction chambercan effectively be avoided when changing the PEALD cycle to the PEALEcycle in the reaction chamber.

In some embodiments, PEALD may be conducted under conditions shown inTable 2 below.

TABLE 2 (the numbers are approximate) Conditions for PEALD Substratetemperature Same as in PEALE Pressure Same as in PEALE (typically 400Pa) Noble gas (as a carrier gas Same as in PEALE and/or dilution gas)Flow rate of carrier gas Same as in PEALE (continuous) Flow rate ofdilution gas Same as in PEALE (continuous) Reactant gas O₂, CO₂, N₂OFlow rate of reactant gas 50 to 3000 sccm (preferably 100 to(continuous) 1000 sccm) Precursor gas Bis-Diethyl-Amino-Silane,Tris-Diethyl-Amino-Silane RF power (13.56 MHz) for a 25 to 2000 W(preferably 100 to 500 W) 300-mm wafer Duration of “Si-Feed” 0.1 to 5sec. (preferably 0.1 to 1 sec.) Duration of “Purge” 0.2. to 10 sec.(preferably 0.2. to after “Feed” 1 sec.) Duration of “RF” 0.1 to 10 sec.(preferably 0.5 to 5 sec.) Duration of “Purge” 0.1 to 10 sec.(preferably 0.2 to 1. after “RF” sec.) GPC (nm/cycle) 0.03 to 0.2(preferably 0.08 to 0.2) on top surface

Typically, the thickness of the dielectric film to be etched is in arange of about 50 nm to about 500 nm (a desired film thickness can beselected as deemed appropriate according to the application and purposeof film, etc.). The dielectric film may be used for double-patterning.

In the sequence illustrated in FIG. 2, the precursor is supplied in apulse using a carrier gas which is continuously supplied. This can beaccomplished using a flow-pass switching (FPS) system wherein a carriergas line is provided with a detour line having a precursor reservoir(bottle), and the main line and the detour line are switched, whereinwhen only a carrier gas is intended to be fed to a reaction chamber, thedetour line is closed, whereas when both the carrier gas and a precursorgas are intended to be fed to the reaction chamber, the main line isclosed and the carrier gas flows through the detour line and flows outfrom the bottle together with the precursor gas. In this way, thecarrier gas can continuously flow into the reaction chamber, and cancarry the precursor gas in pulses by switching the main line and thedetour line. FIG. 1B illustrates a precursor supply system using aflow-pass switching (FPS) system according to an embodiment of thepresent invention (black valves indicate that the valves are closed). Asshown in (a) in FIG. 1B, when feeding a precursor to a reaction chamber(not shown), first, a carrier gas such as Ar (or He) flows through a gasline with valves b and c, and then enters a bottle (reservoir) 30. Thecarrier gas flows out from the bottle 30 while carrying a precursor gasin an amount corresponding to a vapor pressure inside the bottle 30, andflows through a gas line with valves f and e, and is then fed to thereaction chamber together with the precursor. In the above, valves a andd are closed. When feeding only the carrier gas (noble gas) to thereaction chamber, as shown in (b) in FIG. 1B, the carrier gas flowsthrough the gas line with the valve a while bypassing the bottle 30. Inthe above, valves b, c, d, e, and f are closed.

The precursor may be provided with the aid of a carrier gas. Since ALDis a self-limiting adsorption reaction process, the number of depositedprecursor molecules is determined by the number of reactive surfacesites and is independent of the precursor exposure after saturation, anda supply of the precursor is such that the reactive surface sites aresaturated thereby per cycle. A plasma for deposition may be generated insitu, for example, in an ammonia gas that flows continuously throughoutthe deposition cycle. In other embodiments the plasma may be generatedremotely and provided to the reaction chamber.

As mentioned above, each pulse or phase of each deposition cycle ispreferably self-limiting. An excess of reactants is supplied in eachphase to saturate the susceptible structure surfaces. Surface saturationensures reactant occupation of all available reactive sites (subject,for example, to physical size or “steric hindrance” restraints) and thusensures excellent step coverage. In some embodiments the pulse time ofone or more of the reactants can be reduced such that completesaturation is not achieved and less than a monolayer is adsorbed on thesubstrate surface.

The process cycle can be performed using any suitable apparatusincluding an apparatus illustrated in FIG. 1A, for example. FIG. 1A is aschematic view of a PEALD apparatus, desirably in conjunction withcontrols programmed to conduct the sequences described below, usable insome embodiments of the present invention. In this figure, by providinga pair of electrically conductive flat-plate electrodes 4, 2 in paralleland facing each other in the interior 11 (reaction zone) of a reactionchamber 3, applying HRF power (13.56 MHz or 27 MHz) 20 to one side, andelectrically grounding the other side 12, a plasma is excited betweenthe electrodes. A temperature regulator is provided in a lower stage 2(the lower electrode), and a temperature of a substrate 1 placed thereonis kept constant at a given temperature. The upper electrode 4 serves asa shower plate as well, and reactant gas (and noble gas) and precursorgas are introduced into the reaction chamber 3 through a gas line 21 anda gas line 22, respectively, and through the shower plate 4.Additionally, in the reaction chamber 3, a circular duct 13 with anexhaust line 7 is provided, through which gas in the interior 11 of thereaction chamber 3 is exhausted. Additionally, a dilution gas isintroduced into the reaction chamber 3 through a gas line 23. Further, atransfer chamber 5 disposed below the reaction chamber 3 is providedwith a seal gas line 24 to introduce seal gas into the interior 11 ofthe reaction chamber 3 via the interior 16 (transfer zone) of thetransfer chamber 5 wherein a separation plate 14 for separating thereaction zone and the transfer zone is provided (a gate valve throughwhich a wafer is transferred into or from the transfer chamber 5 isomitted from this figure). The transfer chamber is also provided with anexhaust line 6. In some embodiments, the deposition of multi-elementfilm and surface treatment are performed in the same reaction space, sothat all the steps can continuously be conducted without exposing thesubstrate to air or other oxygen-containing atmosphere. In someembodiments, a remote plasma unit can be used for exciting a gas.

In some embodiments, in the apparatus depicted in FIG. 1A, the system ofswitching flow of an inactive gas and flow of a precursor gasillustrated in FIG. 1B (described earlier) can be used to introduce theprecursor gas in pulses without substantially fluctuating pressure ofthe reaction chamber.

In some embodiments, a dual chamber reactor (two sections orcompartments for processing wafers disposed closely to each other) canbe used, wherein a reactant gas and a noble gas can be supplied througha shared line whereas a precursor gas is supplied through unsharedlines.

In some embodiments, the PEALE cycle can be performed using the sameapparatus as for the PEALD cycle, which is illustrated in FIG. 1A,wherein an etchant precursor is introduced into the reaction chamber 3through a gas line 31 (also using the system illustrated in FIG. 1B).Additionally, an ashing cycle can also be performed using the sameapparatus as for the PEALD cycle, which is illustrated in FIG. 1A,wherein an oxidizing gas is introduced into the reaction chamber 3through a gas line 32.

A skilled artisan will appreciate that the apparatus includes one ormore controller(s) (not shown) programmed or otherwise configured tocause the deposition and reactor cleaning processes described elsewhereherein to be conducted. The controller(s) are communicated with thevarious power sources, heating systems, pumps, robotics, and gas flowcontrollers or valves of the reactor, as will be appreciated by theskilled artisan.

The present invention is further explained with reference to workingexamples below. However, the examples are not intended to limit thepresent invention. In the examples where conditions and/or structuresare not specified, the skilled artisan in the art can readily providesuch conditions and/or structures, in view of the present disclosure, asa matter of routine experimentation. Also, the numbers applied in thespecific examples can be modified by a range of at least ±50% in someembodiments, and the numbers are approximate.

EXAMPLES Examples 1 and 2 and Comparative Example 1

A silicon oxide film was formed by PEALD on a 300-mm substrate. InExamples 1 and 2 and Comparative Example 1, PEALE was conducted on thesilicon oxide film under the conditions shown in Table 3 below using thePEALE apparatus illustrated in FIGS. 1A and 1B. The sequence used ineach cycle of PEALE is shown in FIG. 2.

TABLE 3 (the numbers are approximate) Comparative Example 1 Example 1Example 2 Film to be etched (300-mm PEALD SiO₂ wafer) RF power (W) 100RF frequency (MHz) 13.56 Etchant C₂F₆ CF₃CH₂OH (CF₃CH₂)₂O (F = 3) (F =6) Bottle temperature (° C.) R.T. Carrier gas Ar Carrier gas flow (slm)2.0 Dilution gas Ar Dilution gas flow (slm) 0.5 Pressure (Pa) 400Temperature (° C.) 100 Etchant pulse (sec): Supply 0.2, 1.0 0.1, 0.30.1, 0.3 time (FIG. 4A) (FIG. 4A) (FIG. 4A) Purge upon the etchant pulse10 (sec) RF power pulse (sec) 5 Purge upon the RF power 0.1 pulse (sec)Etching rate per cycle (nm/ See FIG. 4A See FIG. 4A See FIG. 4A cycle)Number of cycles 200

In Examples 1 and 2 and Comparative Example 1, the etching rate percycle (EPC) was determined when the feed time (supply time) of etchantgas was changed. The results are shown in FIG. 4A. FIG. 4A is a graphshowing the relationship between etching rate per cycle (EPC) (nm/cycle)and etchant gas feed time per cycle (seconds) according to Example 1(“Ex. 1 (F=3)”), Example 2 (“Ex. 2 (F=6)”), and Comparative Example 1(“Comp. Ex.”).

FIG. 4A indicates that each of CF₃CH₂OH (Example 1) and (CF₃CH₂)₂O(Example 2) was chemisorbed on the surface of the substrate since theadsorption was quickly accomplished and reached a plateau thereafter(reaching a saturation point, i.e., self-limiting adsorption). Also, useof (CF₃CH₂)₂O (F=6) in Example 2 significantly increased the EPC, ascompared with CF₃CH₂OH (F=3) in Example 1 and C₂F₆ in ComparativeExample 1. FIG. 4A also indicates that C₂F₆ was not chemisorbed on thesurface of the substrate since the adsorption process was extremelyslow. In FIG. 4A, the adsorption of C₂F₆ appeared to reach a plateau.However, because the EPC was very low even at the plateau, the surfacewas unlikely to have been saturated with C₂F₆ molecules. Also, as shownin FIG. 4B (FIG. 4B is a reference graph showing the relationshipbetween etching rate per cycle (EPC) (nm/cycle) and etchant gas feedtime per cycle (seconds) when changing the flow rate of etchant gas(C₂F₆) according to a different set of comparative examples), when C₂F₆was used as an etchant gas, the EPC even at the plateau varied dependingon the flow rate of C₂F₆, indicating that etching was not performed byadsorbed C₂F₆ molecules, but by residual C₂F₆ molecules remaining in thegas phase of the reaction chamber.

As discussed above, when the feed time of the etchant gas was 0.1 secondfor Examples 1 (F=3) and 2 (F=6), the EPCs were approximately 0.04nm/cycle and approximately 0.09 nm/cycle, respectively, i.e., the EPCincreased when the number of fluorine atoms (F) in gas molecules wereincreased. By using an etchant gas having a higher number of fluorineatoms in its molecules, EPC can be increased.

Example 3 and Comparative Example 2

The ALE process was performed in Example 3 and Comparative Example 2according to Example 1 and Comparative Example 1 above, respectively,except that the 300-mm substrate had a patterned surface having anaspect ratio of about 2 and an opening width of about 30 nm, and thefeed time of the etchant gas was 0.1 second for Example 3 and 0.2.seconds for Comparative Example 2. The results are shown in Table 4below and FIGS. 5A to 5C. The EPC was approximately 0.04 nm/cycle inExample 3, and that was approximately 0.04 nm/cycle in ComparativeExample 2.

TABLE 4 (the numbers are approximate) PEALE PEALE Initial (Com. Ex. 2)(Ex. 3) Top [nm] 21.5 10.7 (−10.8) 15.4 (−6.1) Side [nm] 21.0 17.5(−3.5)  18.6 (−2.4) Bottom [nm] 22.0 11.4 (−10.6) 19.0 (−3.0)Conformality % [S/T] 98% 164% 120%  Conformality % [S/B] 95% 154% 94%

In Table 4, the numbers in the parentheses indicate reductions inthickness as compared with the initial thicknesses. FIGS. 5A, 5B, and 5Care Scanning Electron Microscope (SEM) photographs of cross-sectionalviews of the silicon oxide films wherein FIG. 5A shows the silicon oxidefilm prior to the PEALE cycles, FIG. 5B shows the silicon oxide filmafter the PEALE cycles using C₂F₆ (Comparative Example 2), and FIG. 5Cshows the silicon oxide film after the PEALE cycles using2,2,2-Trifluoroethanol (CF₃CH₂OH) (Example 3). As shown in Table 4 andFIG. 5A, prior to the PEALE cycles, a SiO film 52 a having a thicknessof about 22 nm was deposited on a Si substrate 51, wherein theconformality (a ratio of thickness at a sidewall to thickness on a flatsurface) of the initial film was about 98% relative to the top filmthickness and about 95% relative to the bottom film thickness. InComparative Example 2, as shown in Table 4 and FIG. 5B, in the film 52 bafter the PEALE cycles, a film portion deposited on the top surface(blanket surface) and a film portion deposited on the bottom surfacewere more etched than a film portion deposited on the sidewalls, whereinthe conformality of the etched film was about 164% relative to the topfilm thickness and about 154% relative to the bottom film thickness. ThePEALE cycles were highly directional and performed anisotropic etching.In Example 3, as shown in Table 4 and FIG. 5C, in the film 52 c afterthe PEALE cycles, a film portion deposited on the top surface (blanketsurface), a film portion deposited on the bottom surface, and a filmportion deposited on the sidewalls were substantially equally etched,wherein the conformality of the etched film was about 120% relative tothe top film thickness and about 94% relative to the bottom filmthickness. The PEALE cycles using 2,2,2-Trifluoroethanol were notdirectional and performed rather isotropic etching, since2,2,2-Trifluoroethanol could be absorbed uniformly on the surfacethrough chemisorption. In general, PEALE cycles using a functionalgroup-containing etchant gas can perform isotropic etching at aconformality of about 80% to about 120%, which is substantially equal tothat achieved by PEALD cycles.

Example 4 and Comparative Example 3

The ALE process was performed in Example 4 and Comparative Example 4according to Example 1 (CF₃CH₂OH) and Comparative Example 1 (C₂F₆)above, respectively, except that the feed time of the etchant gas was0.1 second for Example 4 and 0.2 seconds for Comparative Example 3. Theresults are shown in Table 5 below and FIGS. 6A and 6B. FIG. 6A showscolor images of thin-film etched thickness profile measurement by 2Dcolor map analysis of a film according to Comparative Example 3. FIG. 6Bshows color images of thin-film etched thickness profile measurement by2D color map analysis of a film according to Example 3. In the drawings,the scale bar in color from zero (blue) to one (red) indicates relativethickness of a film.

TABLE 5 (the numbers are approximate) PEALE PEALE (Com. Ex. 3) (Ex. 4)In-plane non-uniformity 18% <10% 1σ%

As shown in Table 5 and FIGS. 6A and 6B, when 2,2,2-Trifluoroethanol wasused as an etchant gas in Example 4, etching was performed uniformly,and in-plane uniformity of etching was very high, as compared with C₂F₆in Comparative Example 3. In FIG. 6B, a center portion and a portionnear the bottom in the drawing show singularity. This is due to anuneven plasma distribution inside the reaction chamber, but not due tothe use of 2,2,2-Trifluoroethanol.

It will be understood by those of skill in the art that numerous andvarious modifications can be made without departing from the spirit ofthe present invention. Therefore, it should be clearly understood thatthe forms of the present invention are illustrative only and are notintended to limit the scope of the present invention.

I claim:
 1. A method for etching a layer on a substrate placed in areaction space by an atomic layer etching (ALE) process which comprisesat least one etching cycle, wherein an etching cycle comprises:continuously providing a noble gas in the reaction space; providing apulse of an etchant gas in the reaction space to chemisorb the etchantgas in an unexcited state on a surface of the substrate in aself-limiting manner, said etchant gas being a fluorocarbon gascontaining a functional group with a polarity, said surface of thesubstrate being constituted by an oxide mineral or nitride mineral; andproviding a pulse of a reactive species of a noble gas in the reactionspace to contact the etchant gas-chemisorbed surface of the substratewith the reactive species so that the surface of the layer on thesubstrate is etched.
 2. The method according to claim 1, wherein whileproviding the reactive species of the noble gas, no reactive species ofO₂, H₂, or N₂ are present in the reaction space.
 3. The method accordingto claim 1, wherein the pulse of the reactive species of the noble gasis provided by applying a pulse of RF power discharge between electrodesdisposed in the reaction space, between which the substrate is placed.4. The method according to claim 1, wherein the oxide or nitride mineralconstituting the surface of the substrate is selected from the groupconsisting of SiO₂, SiON, SiN, TiO, TiON, and TiN.
 5. The methodaccording to claim 1, wherein the noble gas continuously provided in thereaction space is provided as a carrier gas for the etchant gas.
 6. Themethod according to claim 1, wherein a purging period is taken betweenthe pulse of the etchant gas and the pulse of the reactive species ofthe noble gas to remove excess etchant gas from the reaction space, anda purging period is taken after the pulse of the reactive species of thenoble gas to remove by-products from the reaction space.
 7. The methodaccording to claim 1, wherein no gas other than the etchant gas flows asan etchant gas throughout the ALE process.
 8. The method according toclaim 1, wherein the layer of the substrate has a recess pattern.
 9. Themethod according to claim 1, wherein the etched layer of the substratehas a conformality of 80% to 120% when the ALE process is complete. 10.The method according to claim 1, wherein the functional group containedin the etchant gas is selected from the group consisting of a hydroxylgroup, amino group, ether group, ketone group, and carboxyl group. 11.The method according to claim 10, wherein the etchant gas is aperfluorocarbon-derivative gas.
 12. The method according to claim 11,wherein the etchant gas is CF₃ROH, C₃F₇ROH, C₃F₇RNH₂, and/or (CF₃R)₂Owherein R represents an alkylene group having one to four carbon atoms.13. The method according to claim 1, further comprising, prior to theALE process, depositing a film on a substrate in the reaction space byatomic layer deposition (ALD), said film on the substrate constitutingthe surface of the substrate subjected to the ALE process, wherein theALD process and the ALE process are conducted continuously in thereaction space.
 14. The method according to claim 13, wherein thereaction space is controlled at a constant pressure throughout the ALDprocess and the ALE process.